The present invention relates to a high frequency circuit module having an antenna attached to a monolithic microwave integrated circuits (hereinafter referred to as MMICs) formed on top and bottom surfaces of a multi-layered dielectric substrate, and more specifically to an antenna device used at high frequencies such as microwaves and millimeter waves.
Millimeter wave radars have been developed as sensors used in an automotive safe driving support system, a most effective means for reducing traffic accidents and congestions, solving environmental issues of exhaust emissions and noise, and bringing a traffic ITS (intelligent transport system) into wider use. In recent years, efforts are being made to develop millimeter wave radars for automotive use. For wider use of the automotive millimeter wave radars on common passenger cars, there are growing demands for reducing the cost and size of high frequency antenna device.
As a high frequency antenna device suited for the automotive millimeter wave radar, a conventional device has a construction in which a film antenna pattern is formed on one surface of a multi-layered ceramic substrate and a high frequency circuit including MMIC is formed on the other surface (see, for example, JP-A-2003-133801 (page 6, FIG. 7)).
The official gazette of JP-A-2003-133801 discloses a high frequency circuit module (RF circuit module) which has an airtight seal lid 4 mounted on the upper surface of a multi-layered dielectric substrate 2 to airtightly seal RF circuit components, such as metal patterns forming single layer capacitors 13, chip components 14 and microstrip lines, in addition to a plurality of MMICs 5-1, 5-2. In the JP-A-2003-133801, the high frequency circuit module designed to reduce radiation loss, passage loss and transmission loss in a millimeter wave transmission line integrates the antenna with the high frequency circuit to reduce the number of constitutional components, thereby realizing the smaller size and reduced cost.
That is, the package structure of the high frequency circuit module disclosed in JP-A-2003-133801, as shown in FIG. 7 of the official gazette, is characterized by an airtight seal lid 4 which is made of a metal or an insulating material surface-plated with a metal to protect MMICs mounted on the high frequency circuit against water in atmosphere and which is soldered to the hard multi-layered dielectric substrate 2 with eutectic solder or the like to form a hermetically sealed package in order to suppress degradation of the millimeter wave RF circuit made up of millimeter wave MMICs 5 due to temperature and humidity environment.